I believe you should add currently available syntax to proposal text:
let c = zip(a,b).reduce(0) { (acc, tuple: (a: Int, b: Int)) in
acc + tuple.a + tuple.b
}
func takesATuple(tuple : (valueA: Int, valueB: Int)) {
print("a: \(tuple.valueA) b:\(tuple.valueB)")
}
Not so nice as proposed, but not so ugly as just tuple.0.
I'm not sure if the proposed feature is adding important improvement to the
language.
On 30.05.2016 0:20, Dennis Weissmann via swift-evolution wrote:
Thanks for everyone participating in this discussion! :)
I’ve drafted a formal proposal, it is available
here:
https://github.com/dennisweissmann/swift-evolution/blob/tuple-destructuring/proposals/0000-tuple-destructuring.md
Please let me know what you think (it would be great if a native speaker
could take a look at grammar and spelling mistakes). Thanks!
Tuple Destructuring in Parameter Lists
* Proposal: SE-NNNN
<https://github.com/apple/swift-evolution/blob/master/proposals/NNNN-name.md>
* Author(s): Dennis Weissmann <https://github.com/dennisweissmann>
* Status: *Awaiting review*
* Review manager: TBD
Introduction
Tuple destructuring is the process of extracting elements from tuples.
This is valid today:
Swift
|let point = (x: 20.0, y: 31.0, z: 42.0) // Approach 1: let x = point.x let
y = point.y let z = point.z // Approach 2: let (x, y, z) = point // For-in
loops support tuple destructuring for (x, y, z) in [point] { // use x, y, z }|
Swift-evolution thread: [Pitch] Tuple Destructuring in Parameter Lists
<http://thread.gmane.org/gmane.comp.lang.swift.evolution/16190>
Motivation
This proposal seeks to generalize this behavior for every use case where
tuples need to be destructured. These are parameter lists in closures and
parameter lists in functions. Consistency is a major goal of Swift but it
is currently only possible to destructure tuples in the above mentioned places.
Proposed solution
Extending tuple destructuring to parameter lists seems natural and improves
consistency in the language.
Closures
Parameters in closures are currently not directly destructable. They can
either be accessed via |.0|, |.1|, etc. or can be destructured by assigning
them to variables in an explicit statement.
It feels natural to do this right in the parameter list itself (just like
with for-in loops).
Swift
|let a = [0,1,2,3,4,5,6,7,8,9] let b = [0,1,2,3,4,5,6,7,8,9] // Allowed
today: let c = zip(a,b).reduce(0) { acc, tuple in acc + tuple.0 + tuple.1 }
// Also allowed today: let c = zip(a,b).reduce(0) { acc, tuple in let
(valueA, valueB) = tuple return acc + valueA + valueB } // Proposed syntax:
let c = zip(a,b).reduce(0) { acc, (valueA, valueB) in acc + valueA + valueB }|
Functions
When it comes to functions this proposal uses Swift's feature of
differentiating between internal and external parameter names.
Swift
|// Allowed today: func takesATuple(tuple: (Int, Int)) { let valueA =
tuple.0 let valueB = tuple.1 // ... } // Proposed syntax: func
takesATuple(tuple (valueA, valueB): (Int, Int)) { // use valueA // use
valueB }|
This design has no visible effects to the call site of a function but makes
it very convenient for the function author to use the tuple's elements
inside the function body.
Impact on existing code
This feature is strictly additive and does not effect current code.
Alternatives considered
Leave it as is destructure in a separate assignment.
- Dennis
On May 11, 2016, at 10:12 AM, Dennis Weissmann via swift-evolution
<swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
Thanks for all your feedback!
This is the current statistic:
Closure syntax: All positive
Function syntax: 3 (or 4) positive, 2 negative
I’ll try to address the concern Geordie and T.J. have.
func takesATuple(someInt: Int, tuple: (valueA: String, valueB: String)) {}
It’s true that you still have the ‚overhead‘ of having to
type /tuple./ before accessing its members. But this is almost always
what I want (hopefully you’d never actually name your tuple ‚tuple‘,
instead it’d be a logical namespace for what it contains). Do you have a
real-world example where you’d need this? To me it seems that in a case
like this the API that produced the tuple would need refining rather
than the language itself.
What you suggest here is not tuple destructuring but using labeled
tuples. And while I’m totally with you that this is for many cases the
better approach, I still think we should introduce it to functions as
well, for consistency and readability reasons.
In the end inconsistency is what led to this thread because tuple
destructuring is already possible today - in for loops:
letstringTuple = [("", "”), ("", "")]
for(i, j) instringTuple {}
That made me wonder if it’s also possible for closures (because I needed
it there - and eventually someone will definitely wonder if it’s possible
for function arguments as well).
You also asked me for my use case. To be honest, I don’t have one for the
function version, but imagine the following:
My current closure use case is this
(template.points and resampledPoints are of type [CGPoint]):
letlocalHighestSimilarity = zip(template.points,
resampledPoints).reduce(0.0) { accumulator, points in
let(template, resampled) = points
returnaccumulator + Double(template.x* resampled.x+ template.y*
resampled.y)
}
To reuse this code elsewhere I maybe want to refactor the closure into a
function (using your labeled tuple suggestion):
funcaccumulateSimilarity(accumulator: Double, for points: (point1:
CGPoint, point2: CGPoint)) -> Double{
returnaccumulator + Double(points.point1.x* points.point2.x+
points.point1.y* points.point2.y)
}
This isn’t particularity readable (image passing a CGRect and you need
the points or a more complex calculation). Compare it to this:
funcaccumulateSimilarity(accumulator: Double, for (point1, point2):
(CGPoint, CGPoint)) -> Double{
returnaccumulator + Double(point1.x * point2.x + point1.y * point2.y)
}
You can of course still pass a named tuple instead of an unnamed, but it
doesn’t make any difference, which brings me to an aside*.
I think the second approach makes the calculation much more
comprehensible and it just feels “intuitive” (again, at least for me) :).
- Dennis
* I’m not sure how scientifically correct the following statement is but
strictly speaking (at least for me) (valueA: String, valueB: String) is
not of the same type as (String, String) just like func d(string: String,
int: Int) is different from func e(_: String, _: Int) though in Swift the
tuples are interchangeable (you can pass one where the other is expected).
On May 8, 2016, at 6:10 PM, Geordie J <geo...@gmail.com
<mailto:geo...@gmail.com>> wrote:
Comments below
Am 05.05.2016 um 20:22 schrieb Dennis Weissmann via swift-evolution
<swift-evolution@swift.org <mailto:swift-evolution@swift.org>>:
Following a short discussion with positive feedback on
[swift-users](http://thread.gmane.org/gmane.comp.lang.swift.user/1812)
I’d like to discuss the following:
Tuples should be destructible into their components in parameter lists.
Consider the following code:
let a = [0,1,2,3,4,5,6,7,8,9]
let b = [0,1,2,3,4,5,6,7,8,9]
let c = zip(a,b).reduce(0) { acc, tuple in
acc + tuple.0 + tuple.1
}
tuple is of type (Int, Int).
The problem is that the calculation is not very comprehensible due
to .0 and .1. That’s when destructuring tuples directly in the
parameter list comes into play:
let c = zip(a,b).reduce(0) { acc, (valueA, valueB) in
acc + valueA + valueB
}
+1 I think this is a great way to go about it.
The above is what I propose should be accepted by the compiler (but
currently isn’t).
Currently tuple destructuring is possible like this:
let c = zip(a,b).reduce(0) { (acc, tuple) in
let (valueA, valueB) = tuple
return acc + valueA + valueB
}
This is not about saving one line ;-). I just find it much more
intuitive to destructure the tuple in the parameter list itself.
Agreed
The same thing could be done for functions:
func takesATuple(someInt: Int, tuple: (String, String))
Here we also need to destructure the tuple inside the function, but the
intuitive place (at least for me) to do this would be the parameter list.
In the following example I'm making use of Swift’s feature to name
parameters different from their labels (for internal use inside the
function, this is not visible to consumers of the API):
func takesATuple(someInt: Int, tuple (valueA, valueB): (String, String))
I’m not such a fan of this though. I realize what I’m about to write
here is discussing a slightly different point but bear with me: I was
under the impression it was already possible to do something like this
(maybe only possible with typealiases):
func takesATuple(someInt: Int, tuple: (valueA: String, valueB: String)) {}
I find that syntax readable and extensible: you can make a type alias
for your tuple type '(valueA: String, valueB: String)‘, you can then use
it like this:
func takesATuple(someInt: Int, tuple: MyAliasedTupleType) {
print(tuple.valueA)
}
It’s true that you still have the ‚overhead‘ of having to
type /tuple./ before accessing its members. But this is almost always
what I want (hopefully you’d never actually name your tuple ‚tuple‘,
instead it’d be a logical namespace for what it contains). Do you have a
real-world example where you’d need this? To me it seems that in a case
like this the API that produced the tuple would need refining rather
than the language itself.
Here valueA and valueB would be directly usable within the function.
The tuple as a whole would not be available anymore.
Now it’s your turn!
1. What do you think?
2. Is this worth being discussed now (i.e. is it implementable in the
Swift 3 timeframe) or should I delay it?
Cheers,
- Dennis
_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org <mailto:swift-evolution@swift.org>
https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org <mailto:swift-evolution@swift.org>
https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution
